All sounds have a shape, and this shape is really important for what we hear.
The Life of a Sound
Every sound has a beginning, a middle and an end. All sounds change over time.
Changes over the life of a sound are described by the ‘envelope’.
Different sounds have different envelopes. The shape of the envelope affects the sound that we hear.
The shape of a sound’s envelope will affect how it sounds.
When composing, try to use a range of sounds that have different envelopes. This will give your compositions a range of different sound types, and help you to create interesting contrasts (see also: TimbreThe colour or quality of a sound. A combination of all other properties that makes each sound unique. Timbre).
Breaking Down the Envelope
To help us talk about sound envelopes, we can break them down into four clear sections:
- Attack – The speed with which a sound begins.
- Decay – The time it takes for the attack to drop to a steady state.
- Sustain – A steady period in the life of a sound.
- Release – The gradual decay into silence.
Every sound will naturally have these sections, but in different proportions (N.B. some sounds will have only two or three of these section types).
The two most important aspects of the envelope are the Attack and Sustain. Let’s look at these in more detail:
Sometimes the attack might be very short, other times it might be long. The attack is one of the most important parts used by the brain when it tries to recognise sounds.
This sound has a fast attack. Listen to how it very quickly begins. It has a very sharp and crisp sound.
This sound has a slow attack. You can hear how it slowly emerges. It has a very soft and smooth sound.
Sounds with a fast attack are crisp, while those with a slow attack appear more smooth and rounded.
Sounds that ring out have a long sustain.
This sound has a long sustain. Listen to the steady tone.
But if we reduce the sustain, we focus attention on the attack.
The sound does not ring out, but begins to fade away almost immediately.
Sounds with a long sustain will ring out for a long time. Sounds with a short sustain will be very short and quick.
If we listen to the sound of a bell, we can hear its long resonant sustain.
This bell sound has a long sustain, continuing to ring out for a long time as its vibrations slowly dies out.
But, if we dampen that same bell by pressing a cloth against it, we remove all of that sustain and keep mainly the attack.
This time, the cloth prevents the bell from vibrating and ringing out. It dampens the sustain and almost stops it completely.
By dampening the vibrations with a cloth, we have changed the envelope of the bell sound and highlighted the attack of the sound.
Information About the Other Parts of the Envelope
Finally the sound fades out. We often pay a lot of attention to how sounds begin and ignore the way in which they end.
However, the duration of release can make a difference to the sound that we hear.
A sound with a long release will last for a long time and gradually fade out. While sounds with a short release will fade quickly.
Transformations of the Envelope
Because the envelope is a really important property of sound, changes and transformations which affect a sound’s envelope have a big impact on the final sound that we hear.
When we reverse a sound, we flip the envelope. So the attack becomes the release and what was the release becomes the attack.
Listen to the envelope of this original sound. There is a fast attack, followed by a slow decay - sustain - release.
This sound has been flipped in reverse, so the envelope is now backwards. In contrast to the original sound, we now have a slow attack, followed by a quick decay - release. (There isn't even really any sustain at all).
Reversed sounds are used quite a lot in different styles of music. The flipping of the envelope makes a big difference and can create some really fantastical new sounds.
Splicing a sound can allow us to remove or rearrange individual parts of the sound’s envelope. By removing portions of the envelope, we can dramatically transform how we hear a sound.
This sound has a clear and strong attack sound. You can hear the 'thwack' as the glass is hit.
Because the attack is one of the most important pieces of information used by the brain in recognising where a sound comes from, by removing the attack, we can hide the source of the sound.
This sound has had the attack portion spliced off. We no longer hear the loud 'thwack' of the glass being hit, only the ringing sustain of the glass.
Removing (or transforming) the attack portion of a sound’s envelope can help us to hide the original source of the sound, and can focus the listener’s attention on different aspects of the sound.
The shape of a sound envelope is directly related to how an object vibrates and makes sound. The properties of the object and the way in which it is encouraged to make sound will all affect the properties of the final envelope.
For example: Think of the difference in sound between plucking a string (to get a sharp, pizzicato sound) and bowing a string (to get a smooth, steady sound).